The discovery of a headless body in Lake Michigan points to Hank's mob connections. Roman risks everything to help a grieving mother.

When a young officer is shot dead in the lobby of an apartment building, Intelligence looks to the latest known offenders who have threatened the police. But when a second officer is killed, the team finds that they are dealing with someone who is highly trained and knowledgeable.

While investigating a drug-related homicide, Intelligence is stonewalled by the 'no-snitch' culture of the neighborhood. And Atwater discovers a personal connection to the case. Meanwhile, the police's own code of silence is put to the test when Upton is asked about Ruzek's rough altercation with a suspect.

When a gang from El Salvador infiltrates Chicago, Intelligence works with a visiting detective to put an end to the crew's brutal tactics. Meanwhile, Antonio finds himself getting close to Salvadoran Detective Marcella Gomez and Voight learns that the body of his son's killer has been found.

When a prominent Alderman known for his urban revitalization efforts is killed, Intelligence looks into the corruption haunting his neighborhood. Meanwhile Olinsky feels pressure after receiving an ultimatum from Woods.